Embodiments of the present disclosure relate to a semiconductor device and a method for fabricating the same, and more particularly to a semiconductor device having passing gates that prevents characteristics of a cell transistor from being deteriorated by the passing gate effect, and a method for fabricating the same.
In order to increase the degree of integration of a semiconductor device, the size of cell transistors are reduced. More specifically, as semiconductor devices are being developed to implement higher levels of integration, a preferred cell layout is changing from an 8F2 structure to a 6F2 structure.
As the degree of integration of semiconductor devices increases, the distance between a gate (word line) coupled to a cell transistor and a bit line coupled to the cell transistor is reduced. As a result, parasitic capacitance between the bit line and the gate may increase such that the operational reliability of the semiconductor device deteriorates. In order to improve the operational reliability of highly integrated semiconductor devices, a buried gate structure has been proposed in which a gate is buried within a semiconductor substrate. A conventional buried gate structure can be incorporated within a semiconductor device having a 6F2 layout, and can include a metal film as a gate electrode.
However, in a conventional buried gate structure, a portion of the buried gate electrode is disposed on the same level as a junction region that is adjacent to the buried gate. This causes Gate Induced Drain Leakage (GIDL) to occur where the buried gate electrode is on the same level as the junction region. More specifically, when a gate of a cell array of the semiconductor device is a line type gate, a portion of the buried gate disposed in a device isolation film and adjacent to an active region, which is referred to as a passing gate, is present in a conventional device. The passing gate may exacerbate the occurrence of GIDL. The GIDL discharges charges stored in the cell array, thereby deteriorating retention characteristics of the semiconductor device.